1. Field of the Invention
This invention relates generally to an automatic high-speed electro-optical inspection system, and more particularly, to a system including an unique inspection table, movable carriage, optical assembly and a light sensitive array which is adapted to automatically scan, verify, measure and document the perimeters and holes formed in a flat sheet metal workpiece.
1. Prior Art
It is common practice to manually inspect punched, flat sheet metal workpieces using scales, calibers, micrometers on other manual instruments. Complex workpieces with complex shapes and/or a multitude of holes becomes laborious, time consuming and highly subject to human error.
Accordingly, automatic electro-optical inspection systems have been developed to increase efficiency, accuracy and reduce the costs of inspection. However, such automatic systems usually involve the X and Y axis movement of the workpiece or light sensor, reading out the coordinate of each edge crossing as it passes by the center of the sensor. Such systems are generally very slow and expensive.
Another example of prior art is a system employing array multiple linear sensors as described in U.S. Pat. No. 4,711,579, dated Dec. 8, 1987 to Blair E. Wilkinson. This system consists of a transparent table surface, with a yoke which moves in one axis along the table. It employs a plurality of linear sensor CCD arrays (five or more), arranged to form a continuous line of optically alinged CCD sensor arrays arranged to electrically scan across the width of the table. Typically each sensor array consists of a single row of 2048 sensor elements. These arrays are mounted onto a yoke which is mechanically moved in one-axis perpendicular to the direction of array scan. The accuracy of this invention is dependent upon the number of CCD sensor arrays employed. In viewing a typical 48 inch wide scanning format a minimum of eight and preferably sixteen overlapping optical sensor arrays would required to approach the accuracies required by the sheet metal industry. The accuracy of this invention is also dependent upon the workpiece being close to a perfect workpiece, i.e. essentially flat, with sharp vertical walled edges and holes. However, the vast majority of sheet metal workpieces in the industry are sheared and punched, resulting in a workpiece that is slightly bowed, with rounded edges and holes due to tool impact and breakout (hole burst and/or burrs). Tool impact imperfections varies with the type of material, material handling and tools applied. Some workpieces are fabricated with countersunk and dimpled holes. The accuracy of the Wilkinson invention can be significantly degraded by these edge variations because of the angular field-of-view inherent in the systems optics. Holes smaller in diameter then the thickness of the workpiece may not be detectable. The transparent glass/plastic table top cannot be maintained in flat horizontal plane over a large area (as it bows towards the center) and the workpiece will typically lie in a plane above or below the plane of scale calibration. This may be compensated for by overlapping the field-of-views so that each edge is viewed by two optical sensor arrays. Such a system is generally expensive, and requires a very precise and difficult to achieve alignment of the sensors and their optics.
Other examples of known systems for inspecting flat sheet metal workpieces are available in one or more of the following U.S. Pat. Nos:
2,684,009 Jul. 20, 1954 PA1 4,319,272 Mar. 9, 1982 PA1 4,555,798 Nov. 26, 1985 PA1 4,560,273 Dec. 24, 1985